Best way to accurize a mini 14 is to sell it for what you can get for it and buy an AR.

That out of the way, I shot prone "full-bore" match for most of my teens and 20's until I moved to the USA.
I shot a Sportco M44 single shot bolt from 300-500 yards, then switched to a Modified Lee enfield No 4 Mk I for 600-1000(or 1200).